Differential Effects of Lead and cAMP on Development and Activities of Th1- and Th2-Lymphocytes1

Yong Heo 0 1 2 William T. Lee 0 1 2 David A. Lawrence 0 1 2 0 ' This work was supported by NIH Gram ES 03179. Box 509, Albany, NY 12201-0509. Fax: (518) 474-1412 1 Wadsworth Center, New York State Department of Health , Albany, New York 12201 2 HEO , LEE, AND LAWRENCE - Differential Effects of Lead and cAMP on Development and Activities of Thl- and Th2-Lymphocytes. Heo, Y., Lee, W. T., and Lawrence, D. A. (1998). Toxicol. Sci. 43, 172-185. Lead (Pb) is known to have detrimental effects on the central nervous, hematopoietic, renal, and immune systems. Herein, it is demonstrated that Pb can skew T cell reactivities by preferentially enhancing the development of Th2 cells and inhibiting the development of Thl cells. When naive splenic CD4+ T cells from DOll.lO ovalbumin-specific transgenic (OVA-tg) mice or OVA-tg/RAG2~'~ mice were developed in vitro in the presence of Pb, preferential skewing toward Th2 cells was evident. The Pb-driven skewing toward Th2 was blocked significantly in the presence of exogenous IL-12 or anti-IL-4 mAbs. Although Pb and dibutyryl cAMP (dbcAMP) appear to have similar effects on the development and reactivity of Thl cells, unlike Pb, dbcAMP did not enhance Th2 development/activity. Further evidence of Pb's differential T cell effects was observed, in that regardless of the activation stimuli (Ag/APC; anti-CD3; PMA + ionomycin), the addition of PbCl2 consistently resulted in significant inhibition of IFNy production by a Thl clone and in increased IL-4 production by a Th2 clone. In vitro addition of IL-12 overcame Pb's inhibition of Thl cells. Thl cells treated with a phosphodiesterase inhibitor had significantly elevated [cAMP], levels following anti-CD3 activation in the presence of Pb, suggesting that Pb may inhibit Thl development by enhancing adenylate cyclase activity and elevating the [cAMP], level. Similar to Pb, a low concentration (10 (iM) of dbcAMP inhibited IFNy production by Thl, which was prevented by IL-12; however, inhibition of protein kinase A activity by KTS720 did not reverse these effects. These results indicate that the environmental toxicant Pb can modify immune reactivities by significantly altering the differentiation of precursor or naive Th cells as well as by directly inhibiting Thl cells and stimulating T h 2 Cells. O 1998 Sodttj of ToilcoJogy. Key Words: Thl; Th2; cellular activation; cellular differentiation; signal transduction; lead. Helper T cells have been subdivided into at least two distinct subsets based on the pattern of cytokine secretion; type-1 T cells (Thl; Tel)3 produce IL-2, IFNy, and TNF/3, but not IL-4, IL-5, or IL-6, while type-2 T cells (Th2; Tc2) produce IL-4, IL-5, IL-6, and IL-10, but not IL-2 or IFNy (Kurt-Jones et al., 1987; Swain et al, 1991). Studies on factors determining development of precursor (Thp) or naive (ThO) helper T cells into Thl and Th2 mainly have been focused on intrinsic factors of T cells or endogenous, extracellular factors such as cytokines. Initial exposure of CD4+ murine T cells to IL-4 or IL-12 is known to influence differentiation of ThO cells into Th2 or Thl phenotypic effectors, respectively (Hsieh et al., 1992; Sedar et al., 1993). Heat-killed Listeria monocytogenes also was reported to facilitate Thl development in vitro through IL-12 production by macrophages (Hsieh et al., 1993), and IL-12-induced protective Thl responses were proposed for resistance to Leishmania major infections in vivo (Giiler et al, 1996). Thl and Th2 cells are known to be activated by different signals. An activator of adenylate cyclase, prostaglandin Ej (PGE2) or Ej, is known to enhance intracellular cAMP ([cAMP],) levels, leading to inhibition of Thl activation, but not Th2 activation (Betz and Fox, 1991; Naito et al, 1996). Preferential differentiation to Th2 cells by PGEj was reported with human naive CD4+ T cells (Katamura et al, 1995), but has not been reported with murine cells. Currently, it is believed that Th 1 and Th2 cells use different intrinsic pathways to transmit signals from the cell surface to nucleus in response to mitogenic stimulation, in that protein kinase C (PKC) activation and intracellular free Ca2+ ([Ca2+];) increases are not essential for Th2 cell activation (Munoz et al., 1990b; Williams et al, 1991), and different kinds of STAT (signal transducer and activator of transcription) proteins are activated by EL-4, 3 Abbreviations used: Pb, lead; OVA-tg, DOll.lO ovalbumin transgene; RAG2, recombinase activating gene 2; dbcAMP, dibutyryl cAMP; APC, antigen-presenting cells; PMA, phorbol 12-myristate 13-acetate; [cAMP],, intracellular cAMP; Thp, precursor helper T cell; Thl, helper T cell type 1; Th2, helper T cell type 2; PGEj or PGE,, prostaglandin Ej or E,; PKC, protein kinase C; [Ca2+];, intracellular free Ca3+; STAT, signal transducer and activator of transcription; RGG, rabbit IgG; IBMX, 3-isobutyl-l-methylxanthine; PKA, cAMP-dependent protein kinase A; TCR, T cell receptor. IFNy, or IL-12 treatment (Darnell et al, 1994; Szabo et al., 1995; Shimoda et al., 1996). Differentia] influences of heavy metals on helper T cell activities have been demonstrated with mercury and Pb. Both metals inhibit Thl cells and enhance Th2 cells, which lead to an imbalance between Thl and Th2 cells causing aberrant cell-mediated immunity or humoral immunity that may culminate with an autoimmune disease or increased incidence of infectious diseases (McCabe and Lawrence, 1991; Pelletier et al, 1994; Prigent et al., 1995; Heo et al, 1996). While Pb inhibits the proliferation of murine Thl clones, it enhances that of Th2 clones, and Pb preferentially activates Th2 responses in vivo, ex vivo, and in vitro (McCabe and Lawrence, 1991; Heo et al, 1996, 1997). Furthermore, Pb can downregulate cellmediated immunity by inhibition of macrophage development and activation (Kowolenko et al, 1988; Tian and Lawrence, 1995) and simultaneously enhance humoral immunity by induction of B cell differentiation and activation (Warner and Lawrence, 1986; McCabe et al, 1991; Guo et al, 1996). Recently, it also was reported that the inhibitory effects of Pb on mouse resistance to Listeria could be overcome by IL-12 treatment (Kishikawa et al, 1997), but the intracellular mechanisms of Pb-induced differential effects on Thl and Th2 cells as well as the influences of Pb on the development of naive helper T cells have not been reported. In light of the results demonstrating Pb enhancement of type-2 responses, determination of whether Pb would preferentially skew naive T cells toward Th2 cells and understanding the mechanisms by which environmental agents, including Pb, establish an imbalance between type-1 and type-2 reactivities are vital since disorders such as asthma and AIDS worsen when type-2 responses dominate. Hypothetically, an environmental agent may predispose an individual toward a more pathological outcome by shifting the T-cell-dependent immunoregulatory balance. In this report, Pb effects o (...truncated)